Switches are known which are actuatable between a first position and a second position. Such switches, especially for low current loads and voltage levels, can comprise a snap action member which is bistable, that is, having a first stable position electrically engaging a first stationary contact, and a second stable position electrically engaging a second stationary contact. In one type, a snap action member stresses itself against one or the other of the stationary contact members with contact normal force, and an actuator stresses the snap action member during actuation coincidentally reducing the existing contact normal force of the member against an initial one of the contacts, until the flex point is reached at which the member flexes or snaps from its initial or first stable position to its resulting or second stable position. In another type, as disclosed in U.S. Pat. No. 4,417,106 a spring-loaded actuator is used with a seesaw movable contact whose center point rests on a fulcrum, the actuator providing the source of the contact normal force of a first end of the movable contact against a first stationary contact; the actuator is moved along the movable contact and over the center point thereof, removing the force against the first end, and snapping against the second end of the movable contact to urge it against a second stationary contact under contact normal force.
However, such snap action is not truly instantaneous but instead is comprised of a short period of snapping preceded by a very short period of disengagement from the first contact, and followed by an even shorter period of becoming engaged with the second contact. It is known that the longer the time it takes the snap action member or movable contact member to disengage, the more likelihood and extent of damage to the contact surfaces by reason of the reduction of contact normal force between the contact surfaces during that time. Such reduced contact normal force is known to reduce the real area of contact between the metal surfaces which microscopically comprises facing densely packed arrays of structures known as asperites, having varying heights; at a reduced contact normal force fewer and fewer asperites (the higher ones) engage each other and they continue carrying the electrical load originally carried by all. Such relative increase in the load on the last remaining asperites before complete disengagement results in points of constriction resistance and highly localized heating and melting due to current, and after complete separation electrical arcing with vaporization and burning due to voltage. Some prior switches sought to minimize damage to contacts by using buttons of a erosion-resistant precious metal alloy which served as local heat sinks but provide limited contact surface area. Such buttons are secured firmly on ends of spring arms made of a metal alloy selected for its spring properties but having reduced electrical conductivity, and the structure of the spring arms has low mass for speed of snapping and therefore has limited current-carrying and heat sinking capability. At best the prior art switches are compromises between seemingly contradictory goals.
It is desirable to provide a switch which not only has a very short period of engagement, but which also shortens the period of disengagement from the initial contact and also retains the full contact normal force for as long as possible. It is also desirable to eliminate the need for expensive precious metal alloys by minimizing the causes of erosion. It is also desirable to provide a large mass for heat dissipation. It is still further desirable to provide a switch which is easy to assemble, and easy to mount to a panel. In general, it is desirable to provide an economical and durable switch for mid-range current and voltage loads.